Dispatch service architecture framework

ABSTRACT

Group voice services are provided in a wireless network, such as a cellular telephone network ( 104, 108, 116 ), by a dispatch gateway ( 102 ) that interfaces to the wireless network to provide the group voice services therein, wherein both the dispatch gateway and mobiles ( 120 ) that use the group voice services communicate with each other using cell setup and in-band signaling within the wireless network.

CROSS RNCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. Section 119(e) ofthe following co-pending and commonly-assigned U.S. provisional patentapplications:

Ser. No. 60/382,981, filed on May 24, 2002, by Gorachand Kundu, RaviAyyasamy, and Kris Patel, entided RADIO GATEWAY ARCHITECTURE FRAMEWORK,attorneys' docket number 154.3-US-P1;

Ser. No. 60/383,179, filed May 24, 2002, by Gorachand Kundu, RaviAyyasamy, and Kris Patel entided DISPATCH SERVICE ARCHITECTUREFRAMEWORK, attorneys' docket number 154.4-US-P1; and

Ser. No. 60/407,168, filed Aug. 30,2002, by Gotachand Kundu, RaviAyyasamy, and Kris Patel, entitled DISPATCH SERVICE ARCHITECTUREFRAMEWORK, attorneys' docket number 154.5-US-P1;

all of which are incorporated by reference herein

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to wireless communications systems,and more specifically, to a dispatch service providing “push-to-talk”service in a cellular telephone system.

2. Description of Related Art

Group-based dispatch services (two-way half-duplex voice calls within agroup also known as “Push-to-Talk” or PTT) have enormous revenueearnings potential for wireless networks, such as cellular networks andpersonal communications systems (PCS) networks. Corporate subscribersprimarily use such services for coordinating field people or fleet usersfrom a central location.

Currently, there are two major approaches employed in providing dispatchservices such as PTT in wireless networks. One approach requires theinstallation of a dedicated private network, parallel to the wirelessnetwork, to support dispatch services. Nextel™ uses such a system, basedon a solution developed by Motorola™ known as iDEN™. However, adedicated private network is costly to install and maintain employed bya few public wireless carriers,

Another approach is based on Voice over IP (VoIP) technologies. Whilethis approach promises compliance with newer and emerging standards,such as GPRS (General Packet Radio Service), UMTS (Universal MobileTelecommunications System), etc., it does not provide a solution forcarriers employing wireless networks based on existing standards, suchas GSM (Global System for Mobile Communications), CDMA (Code DivisionMultiple Access), etc. Even for the newer standards, solutions based onVoIP have serious drawbacks as explained below.

1. Call Setup: VoIP based solutions suffer from slower call setup, sincethis is a serial process. For example, for a CDMA PTT solution, callsetup involves a CDMA data channel setup, followed by a PTT setup withSIP (Session Initiation Protocol) signaling. There is a need, instead,for parallel call setup exploiting existing cellular solutions.

2. Maximum Information Throughput Rate: VoIP solutions result insignificant overhead to carry voice over data channels resulting insignificantly reduced net information throughput rate.

3. Impact of Packet Loss: VoIP solutions employ voice packet aggregationthat results in increased susceptibility to packet losses.

4. Voice Quality: VoIP solutions employ low bit rate voice coders (4kbps). There is a need, instead, for an approach that complies withhigher rate voice coders, such as EVRC (Enhanced Variable Rate Codec),resulting in better voice quality.

5. Impact to Mobile Handsets: VoIP solutions require significantmodifications to the mobile handset. There is a need, instead, forsolutions that require only minimal upgrades to the handset.

In summary, there is a need in the art for dispatch services solutionsthat comply with existing and emerging wireless standards and providessuperior user experience with faster call setup, better voice quality,and improved information rate compared to other competing solution.

The present invention aims to satisfy these needs by providinggroup-based dispatch services that use existing networks with minimalchanges. The dispatch service architecture framework of the presentinvention allows the wireless network to provide an instantaneous voicemessaging service wherein a group of users can exchange voice messagesat any time from anywhere within the network. This powerful, innovativeand cost-effective dispatch service architecture framework willdifferentiate the service offerings by present wireless networks andprovide them edge over their competitors.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesan apparatus for providing group voice services in a wireless network,comprising a dispatch gateway that interfaces to the wireless network toprovide the group voice services therein, wherein both the dispatchgateway and mobiles that use the group voice services communicate witheach other using call setup and in-band signaling within the wirelessnetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a block diagram that illustrates an exemplary embodiment ofthe dispatch services architecture framework according to a preferredembodiment of the present invention;

FIG. 2 is a block diagram that illustrates the protocol stacks for thedispatch call control plane services according to a preferred embodimentof the present invention;

FIG. 3 is a block diagram that illustrates the protocol stacks for theinter-DG group call signaling according to a preferred embodiment of thepresent invention;

FIG. 4 is a block diagram that illustrates the protocol stacks for thebearer plane for a dispatch call from the mobile to the dispatch gatewayaccording to a preferred embodiment of the present invention;

FIG. 5 is a block diagram that illustrates the major functional blocksin the dispatch gateway according to a preferred embodiment of thepresent invention;

FIG. 6 is a state diagram that illustrates the functions of the groupvoice application according to a preferred embodiment of the presentinvention;

FIG. 7 is a block diagram that illustrates the call flow for a VoiceGroup Call in a CDMA network according to a preferred embodiment of thepresent invention; and

FIG. 8 is a block diagram that illustrates the call flow for a VoiceGroup Call in a GSM network according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration the specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized as structural changes may be made withoutdeparting from the scope of the present invention.

Definitions

This section provides a brief definition of the functional components.The components are described with respect to their base functionalityand are not specific to their hosting platform.

Dispatch Service (DS): The dispatch service is defined as an instanttwo-way half-duplex voice messaging within a group of users. Any userwithin the dispatch service network can join any group (provided he/shehas privilege) and talk to the group members from anywhere in thenetwork. It is also called as Push To Talk (PTT) service.

Dispatch Gateway (DG): The dispatch gateway combines both bearer andsignaling functions of the group voice service. Physically, it is asingle node or system control point that enables a carrier to introducegroup voice service into its network. It does not have any interface toradio access technology. The main purpose of this system is to supportall group call signaling including SS7-ISUP (Signaling System7-Integrated Services Digital Network User Part) signaling, callprocessing and voice frame duplication functions. For PTT calls spanningacross multiple DGs, it uses packet technology. It uses SIP (SessionInitiation Protocol) for signaling and RTP/UDP/IP (Real-time TransportProtocol/User Datagram Protocol/Internet Protocol) for voice transportfor inter-DG PTT calls.

Registration and Presence Application (RPA): The registration andpresence application enables group voice service users to track thepresence of fellow members in the network on their mobile handsets. Whena user powers on/off his mobile, his presence is updated in fellowmembers' handsets within the group.

Tandem Free Operation (TFO): Tandem free operation refers to an in-bandsignaling standard through PCM (pulse code modulation) frames to bypassvoice coders for mobile-to-mobile calls. TFO improves MOS(mean-opinion-score) for mobile-mobile calls, as they don't requireunnecessary vocoder conversion at egress (e.g., wireless codec to PCMand ingress points (e g., PCM to wireless codec).

Architectural Overview

In the present invention, group-based dispatch services are providedthrough existing circuit-based wireless network infrastructures. Thegroup-based dispatch services interface into the wireless network inorder to provide group call signaling and voice frame duplication.Consequently, this present invention does not require any change in theexisting wireless network infrastructure, and only requires minorapplication level changes in mobile handsets.

This application describes the dispatch service architecture frameworkin more detail below. It discloses a high-level network topology thatincludes a dispatch gateway and the interfaces required for providingthe dispatch services. It also shows the call flows for group calls madewithin the network.

Network Architecture

FIG. 1 is a block diagram that illustrates an exemplary embodiment ofthe dispatch services architecture framework according to a preferredembodiment of the present invention.

Within the network 100, a DG (dispatch Gateway) 102 communicates with aMSC (Mobile Switching Center) 104 and PSTN (Public Switched TelephoneNetwork) 106 using SS7-ISUP/WIN/CAMEL (Signaling System 7-IntegratedServices Digital Network User Part/Wireless IntelligentNetwork/Customized Applications for Mobile Enhanced Logic) messages at asignaling plane 108. A bearer path 110 implements a TDM (Time DivisionMultiplexing) interface carrying PCM or TFO voice frames. Support forTFO in this path 110 is negotiated between a BSC (Base StationController) 112 and the DG 102 for each originating and terminating legof a group call. The use of TFO ensures high voice quality (as voicecodec conversion is avoided) between mobile-to-mobile calls. Using TFO,the network can achieve higher MOS scores for PTT calls.

When a subscriber originates a group call the MOS 104 routes the call tothe DG 102. The MSC 104 also requests the BSC 112 via 116 to establish aradio traffic path 118 with the mobile 120 via the BTS (Base TransceiverStation) 122 (as it does for a normal cellular call). At this time, theBSC 112 tries to negotiate TFO (if it is supported) on a TDM link withthe far end (m this case, the DG 102).

At the same time (after the MSC 104 terminates the group call request tothe DG 102), the DG 102 identifies the terminating group users and theirMS-ISDN (Mobile Station ISDN Number) numbers. It sends a ISUP callorigination request for each terminating mobile 120. It may sendrequests directly to the MSC 104, PSTN 106 or IP network 124 via a PDSN(Public Data Switched Network) 126, Router 128, and/or Internet/Intranet130, depending on the routing table configuration for terminatingMS-ISDN numbers. Once the bearer path 110 is established, the DG 102begins a negotiation with the far end in this case, the terminating BSC112) for each terminating leg to a mobile 120.

Once bearer paths 110 are established for originating and terminatinglegs for a group call, the DG 102 switches (or duplicates) voice framesfrom the originating mobile 120 to all terminating mobiles 120.

The DG 102 may use an IP network 124 or the Internet/Intranet 130 fortwo different purposes. The IP network 124 or the Internet/Intranet 130can be used in a toll bypass mode where two DGs 102 can exchange voicetraffic bypassing the PSIN 106. However, each DG 102 is responsible forterminating traffic to its closest MSC 104. In this case, the IP network124 or the Internet/Intranet 130 is used as a backbone transport ofvoice traffic between two DGs 102.

The IP network 124 or the Internet/Intranet 130 can also be used for aregistration and presence application. Since the MSC 104 will not directa registration request from a mobile 120 to the DG 102 (because it wouldrequire changes in the MSC 104), the latter doesn't have any informationof the registered mobiles 120. To circumvent this issue, a registrationand presence application runs over an IP stack in the mobile 120. Afterthe mobile 120 registers for a data interface (i.e., obtaining an IPaddress) with the PDSN 126, the registration and presence application inthe mobile 120 registers with the DG 102 using its IP address. The DG102 also uses this IP interface to update the presence information ofother group members to a mobile 120. There is also provision to use SMS(Short Message Service) transport to carry presence messages if anoperator chooses to use SMS over a data channel.

During roaming, a Home Location Register (TTR) 132 can be accessed viathe MSC 104 and an IS41 link 134. The HLR 132 can be used to track thepresence of members of a group within the network and updates themobiles 120 for those members wit the network availability of othermembers of the group. This is described in mote detail later in thisdocument.

Protocol Stacks

FIG. 2 is a block diagram that illustrates the protocol stacks for thedispatch call control plane services according to a preferred embodimentof the present invention. The mobile (MS) 120 includes a dispatchapplication, as well as modules for radio frequency (Air), layer 2 (L2)and layer 3 (L3) protocols. The BTS 116 includes a relay application, aswell as modules for Air and T1 protocols. The BSC 112 includes an IOSapplication, as well as modules for T1, L2 and L3 protocols, and variousSS7 protocols, such as MTP-1 (Message Transfer Part Level 1), MTP-2(Message Transfer Part Level 2), MTP-3 (Message Transfer Part Level 3)and SCCP (Signaling Connection Control Part) protocols. The MSC 104includes an IOS and call control application, as well as modules for theT1 protocol and various SS7 protocols, such as the MTP-1, M -2, MTP-3,SCCP and ISUP (Integrated Services Digital Network User Part) protocols.The DG 102 includes a dispatch application, as well as modules for theT1 protocol and various SS7 protocols, such as MIT-1, MTP-2, MTP-3 andISUP protocols.

The mobile (MS) 120 interfaces with the BTS 116 with any of thesupported interfaces, identified as 1X/95. The interface between the BTS116 and BSC 112 is based on the Abis standard. The interface between theBSC 112 and the MSC 104 is based on the IOS standard. However, the DG102 interfaces using standard SS7/ISUP signaling with the MSC 104.

As noted above, the dispatch application resides both in the mobile 120and DG 102. The rest of the elements in the network such as the BTS 122,BSC 112 and MSC 7. 104, are transparent Subsequent to establishing a PITsession, the DG 102 interacts with the mobile 120 through DTMFsignaling.

FIG. 3 is a block diagram that illustrates the protocol stacks for theinter-DG group call signaling according to a preferred embodiment of thepresent invention. In addition to the protocols and interfaces noted inFIG. 2, these protocol stacks include modules for UDP/IP (User DatagramProtocol/Internet Protocol), Ethernet and 10×BT (1000/100/10 Base-T)protocols. The DG 102 uses eended SIP (Session Initiation Protocol) forsetting the group call with the other DG 102, and the inter-DG signalingis performed over the manqged IP network 124.

FIG. 4 is a block diagram that illustrates the protocol stacks for thebearer plane for a dispatch call from the mobile 120 to the DG 102according to a preferred embodiment of the present invention.

The mobile (MS) 120 includes modules for EVRC (Enhanced Variable RateCodec) and Air protocols. The BTS 116 includes modules for EVRC, Air,ATM (Asynchronous Transfer Mode), AAL2 (ATM Adaptation Layer 2) andSSSAR (Specific Segmentation and Reassembly) protocols. The BSC 112includes modules for EVRC Relay, T1, ATM, AAU2, SSSAR and PCM (ITFO)protocols. The MSC 104 includes modules for T1 and PCM (TFO) protocols.The DG 102 includes modules for EVRC Relay, T1 and PCM (IFO) protocols.

For intra-DG call legs, EVRC frames will travel in the same way from theDG 102 to the mobile 120. However, for inter-DG call legs, voice framesare carried over RTP (Real-time Transport ProtocoD /UDP/IP between DGs102.

Functional Blocks in the Dispatch Gateway

FIG. 5 is a block diagram that illustrates the major functional blocksin the DG 102 according to a preferred embodiment of the presentinvention.

1. Group Voice Signaling and Control—This subsystem is involved in thecontrol plane for processing group call requests, communicating with theMSC 104 or PSTN 106, controlling its own bearer path ports and handlingpresence notifications. It consists of following important modules

-   -   SS7 ISUP, WIN, CAMEL Signaling—This module is responsible for        handling all ISUP messages and maintaining ISUP related call        state machines. It routinely monitors the health of TDM circuits        and initiates/terunates ISUP maintenance requests. It interfaces        with group call processing layer to originate or terminate call        requests. The WIN/CAMEL interfaces are used by the MSC 104 to        notify the DG 102 about the dialed digits (group id) when an        origination trigger condition is met. In this way, the DG 102        can start setting up the terminating legs parallel to the        originating leg radio setup. This gives faster group call setup.    -   Group Call Processing and Routing—This module processes group        call requests, maintains call state machines for each        originating and terminating call leg, and routes call according        to the called MS-ISDN numbers. It also interfaces with a group        and subscriber database for retrieving group and subscriber        related information, and validating the subscribers'        authenticity. It also controls the floor of the group call by        allowing only one user to speak at any time during the call        session. A Routing fulnction decides whether the call needs to        be terminated to the MSC 104, PSTN 106 or IP network 124 (Inter        DG call to bypass toll).    -   SIP with Dispatch Extension (DG-DG)—This module enables two DGs        102 to communicate with each other at signaling plane. Two DGs        102 may communicate to establish a call in a toll bypass mode or        to retrieve group information for a group from its home DG 102.        They may also exchange signaling messages during a call session        to indicate call continuation or call re-initiation requests.        Standard SIP message set may need to be modified to suit these        inter-DG group call control features.    -   Voice Session Control Function—This module acts as a media        control agent to perform incoming and outgoing port allocation,        to control voice frame duplication and media switching. It is a        lower layer function to control bearer paths within the system.        It also interacts with bearer the path to generate and receive        DTMF tones. It interfaces with a group call processing layer to        send and receive call control messages.    -   Presence Management—This function handles group service        registration requests and updates group service users with the        presence information (whether fellow group subscribers are using        group service) of fellow group subscribers. This application        runs as a separate entity, and updates group database and sends        notification to mobile nodes. It communicates with a        corresponding application layer in the mobiles 120 through the        IP network 124 (via the PDSN 126). This application may also use        an existing SMS infrastructure to transport registration request        and presence update messages from/to mobile nodes to/from the DG        102, respectively. If the SMS infrastructure is used, the SMS        payload is used to carry the signaling message that contains        information about the type of message received, and a set of        Type/Value pairs. However, this requires the mobile units to        have SMS service that can send mail outside a configured PLMN        (public land mobile network).

2. Voice Bearer Path Components—This subsystem is responsible forhandling voice frames in the bearer path. It also receives and generatesDIMP tones and notifies the media control application. It has followingmajor functional components

-   -   Access Traffic Interface (TFO/PCM)—This module is responsible        for the terminating or originating PCM/TFO interface from/to the        MSC 104 or PSTN 106. It handles TFO negotiation procedures with        originating and terminating BSC 112. Please note that for a        TFO-TFO call (where both originating and terminating legs        support TFO), this function does not modify the voice payload        content In this scenario, it just accepts PCM frames from an        originating port, buffers it for 20 ms, extracts signaling        information (if anything is caaried) and switches the payload to        the terminating legs as a PCM frame (carryng TFO). However, if        any of the leg does not support TFO, this function provides        input to a vocoder conversion function to change the packet        format to PCM for that leg. Please note that all legs of a group        call will support PCM, but some of them may support TEFO (since        TFO requires a BSC 112 upgrade and it is assumed that service        providers may not have upgraded all BSCs 112 in their network at        the time of deployment of group voice service). The DG 102, by        default, will try to negotiate TFO with the remote terminating        BSC 112. If the remote BSC 112 doesn't respond, the DG 102 will        establish a pure PCM interface.    -   DTMF Tone Generation and Reception—In this architecture, the        group voice service application in the mobile 120 and the DG 102        exchange a set of defined in-band DTMF tones as call control        events to regulate the group call. These include an initiating        pause request by the originator, initiating call continuation        request by a user and communicating state change requests to        mobiles 120 by the DG 102. This functional component sits on the        bearer path to detect DTMF tones that are originated by the        group voice service application in the mobiles 120. Once        detected, it notifies the media control function. Similarly,        upon receiving instruction from the media control function, it        generates DTNF tones to be received and analyzed by the        corresponding application in the mobiles 120.    -   Voice Frame Duplication—In the group voice application, voice        frame duplication plays a key role as incoming frames need to be        copied or switched to many outgoing ports. A multicasting        control technique is used whereby it reduces number of frames at        the back plane for internal frame switching and at the same time        minimizes number of packets to be carried to another DG 102        (over the IP network 124) that controls a set of end points of        the group call    -   Vocoder Conversion—A group call can involve legs where some of        them do not support TFO. In that scenario, a vocoder conversion        is needed at the DG 102 between TFO, which carries an EVRC        format payload for CDMA, and EFR/AMR (Enhanced Full        Rate/Adaptive Multi Rate) voice coding for GSM, and PCM. An        alternate solution to vocoder conversion can be to support all        call legs on PCM (every leg supports this as default). But, this        would reduce MOS for call legs that support TFO. It is assumed        that TFO will be introduced in most parts of the network by the        time group service is deployed in the field    -   RTP Processing (Inter-DG Traffic)—Two DGs 102 may get involved        in transporting voice frames over the IP network 124. This is        used to bypass the PSIN 106. In this scenario, the RTP protocol        is used to carry voice frames eitherin the form of TFO/PCM        (G.711) between two DGs 102. Only one RTP stream is used for a        group call between two DGs 102. The receiving DG may internally        connect that single RTP source to many access ports (TDM).        Please note that while sending RTP packet, the source DG 102        does not change the voice payload format The PCM frames        (carrying TFO) are buffered and packetized at 20 ms interval and        sent in an RTP envelope without modifying the content. The        receiving DG 102, depending on supported formats on access legs        (PCM or TFO), may change the payload format    -   QoS (Quality of Service) Support—The DG 102 may require the use        of RSVP (Resource Reservation Protocol) or proprietary QoS        protocols to indicate high priority for delivering packets        carrying voice frames.

3. Group Database—This subsystem is the repository of group subscriberinformation. The Group call processing layer, presence application andother system provisioning components interact with this subsystem.

-   -   Group Information Store—This module stores group related        information keyed against a unique group id. The group        information consists of a set of subscribed members and their        privileges. A group may have members located across different        regions within a national network. The DG 102 that holds this        information for a specific group is called the Home DG 102 for        that group. If a group call request arrives at a DG 102 that        does not hold the requested group information, it identifies the        Home DG 102 of the group and fetches information from there. It        might store that information in its cache temporarily.    -   Subscriber Data—This module stores information of a subscribed        group user keyed against the subscriber MS-ISDN and/or internal        member id. It stores the subscriber's registration information        and the group ids of which he/she is a member. This information        is used by the presence application to send a presence        notification. Please note that the subscriber data does not        include the information about his/her current location. However,        it may be possible to store whether a mobile 120 is in its home        network or outside by comparing the system id that it sends        during group voice registration. This information may be useful        in terminating a call to a user directly instead of going to its        home network.

Group Voice and Presence Application

FIG. 6 is a state diagram that illustrates the functions of the groupvoice application according to a preferred embodiment of the presentinvention.

State 600 represents a mobile 120 in a NULL state, ie., the start of thelogic. A user pressing a PTT button or making a request to terminate agroup call triggers a group voice application.

State 602 represents a mobile 120 in an active group call state: In thisstate, the user receives a chirp tone to start talking. The userresponds by pressing the PTT button on the mobile 120 and talking. Atalking user must hold the PTT button. The group voice application inthe mobile 120 ensures that only when the user presses the PIT button isthe reverse traffic channel is used to send voice frames, and the DG 102switches voice frames only in one direction, i.e., from talker tolistener, which ensures the half-duplex operation required for a PTTcall.

State 604 represents the group “floor” being available to all members ofthe group. When the talking user releases the PTT button, the floor isavailable to all group members. All members of the group receive a “freefloor” tone on their mobile 120. A user who requests the floor bypressing the PTT button first (in the “free-floor” state) is assignedthe floor, wherein the network sends a chirp tone to the successfuluser.

State 606 represents a mobile 120 being in an active group call state.In this state, the user is listening to the group call. If a non-takinguser presses the PTT button in a call active state, the user does notreceive any response from the network and remains in the same functionalstate.

State 608 represents a user receiving an “usuccessful bidding” tone onhis mobile 120, after the user pressed the PTT button, but was notgranted the floor of the group call. The user subsequently startslistening to the voice message of the talking user.

Non-talking users (including the talking user who must release the PTTbutton to end the call thus becoming non-talking and making the flooravailable for others) can request the network to end their respectivecall legs explicitly.

State 610 represents a terminating leg being released from the groupcall after the user ends the call.

State 612 also represents a terminating leg being released from thegroup call after the user ends the call.

State 614 represents all terminating legs being released from the groupcall when no member of the group bids for the floor within a specifiedtime period.

Service Interactions

A mobile 120 can support either cellular or group voice service at anyinstant of time. This section highlights various scenarios when twoservices are crossing paths with each other. In some of these cases, theusers' intervention is needed to select one of the services, whereasother cases are decided by the application itself as part of callprocessing logic. This section also discusses the impact of othercellular services such as call hold, call forwarding, call forwardingbusy, call waiting, call forwarding no answer, etc., on group voiceservice.

The following table is prepared on the basic assumption that, whileusing the group voice service, a user cannot put other parties on hold,even though he can switch to another call without disconnecting hisgroup call session. However, a user can leave the group call session atany time by selecting an “end” key. The objective is to allow groupmembers to continue with the call while one or more legs can either bereleased from the DG 102 or disjoined at the MSC 104 (at the time ofservice switching) during a session. The network releases a group callonly when a floor remains free for a predefined time. If a talking userleaves the session, the network will make the floor available to allothers.

It is also assumed that a group user has call waiting, calling numberpresentation at call waiting, call forwarding busy (to voicemail) andcalling line identity presentation features. TABLE 1 Service InteractionScenarios for Group Voice Application Action by Group Voice and PresenceSI (Service Application in Interaction) Present State (in TriggeringMobile No. Mobile) Event Handset Remarks 1. A group voice call isAnother group (1) In this case, For the first case, in active state andthe or cellular call is the application the user is alive user istalking with the being terminated sends a DTMF as the non- PTT buttonpressed. by the MSC and signal to free the talking leg to a call-waitingfloor. Next, the DG, even tone is played. application sends though theThe user is a FlashwithInfo circuit is broken prompted to message to atthe MSC. The accept the accept the DG may release second call. Thesecond call, while all legs of the call following the first call is atany time. scenarios broken at the can MSC. After happen: (1) heattending the releases the PTT second call, the button and user maytoggle accepts the to first one. second call; (2) (2) In this case, hereleases the application sends PTT button, a DTMF signal ends the activeto free the floor. call and accepts Next it releases the second call;the active call (3) he does not and the second accept the call isestablished waiting call and as defined in continues with procedure2.5.5.2 the first call. of 3GPP2 A.S0001-A, Nov. 30, 2000. (3) The MSCprovides treatment to the second call as a ‘call forwarding no answer’feature provisioned for the user. 2. A group voice call is Another group(1) In this case, in the active state and or cellular call is theapplication the user is non-talking being terminated sends a (does nothold the by the MSC and FlashwithInfo PTT button pressed). acall-waiting message to tone is played. accept the The User is secondcall, while prompted to the first call is accept the broken at thesecond call. The MSC. After following attending the scenarios can secondcall, the happen: (1) he user may toggle accepts the to the first one.second call; (2) (2) In this case, he ends the the application activecall and releases the accepts the active call and second call; (3) thesecond call is he does not established as accept the defined in waitingcall and procedure 2.5.5.2 continues with of 3GPP2 the first call.A.S0001-A, Nov. 30, 2000. (3) The MSC provides treatment to the secondcall as a ‘call forwarding no answer’ feature provisioned for the user.3. A cellular voice call is Another group Similar to the in activestate. call is being previous case. terminated by the MSC and acall-waiting tone is played. The User's action is similar to theprevious case. 4. A group call is in the The User wants (1) In thiscase, In the first case, active state and the to originate theapplication it may lead to a user is talking with the another cellularsends a DTMF 3-party call. The PTT button pressed. call. The signal tofree the 3-party call following floor. Next, the should be scenarios mayapplication sends avoided from the happen: (1) The a FlashwithInfo groupcall User releases message to perspective. PTT button and originate theoriginates the second cellular second call; (2) call, while the the Userreleases first call is the PTT button, broken at the ends the first MSC.After active call and attending the originates the second call, thesecond call (he user may toggle can originate a to the first one. groupcall also). (2) In this case, application sends a DTMF signal to freethe floor. Next, it releases the active call and then originates acellular or group call (by pressing the PTT button). 5. A group call isin the The user wants (1) In this case, active state with the tooriginate the application non-talking user, (the another cellular sendsa PTT button is free). call. The FlashwithInfo following message toscenario may originate the happen: (1) the second cellular useroriginates call, while the second cellular first call is call; (2) theuser broken at the ends first active MSC. After call and attending theoriginates second second call, the call (he can user may toggleoriginate group to the first one. call also). (2) In this case, theapplication releases the active call and then originates a cellular orgroup call (by pressing the PTT button). 6. A cellular voice call is Theuser wants (1) In this case, the active state. to originate a theapplication PTT call. The sends a following FlashwithInfo scenarios maymessage to happen: (1) the originate the user originates second PTT callthe second while the first (PTT) call by call is broken at pressing thePTT the MSC. After button; (2) the attending the user ends the secondcall, the first active call user may toggle and originates to the firstone. the second call (2) In this case, (PTT). the application releasesthe active call and then originates a group call (by pressing the PTTbutton). 7. A group/private call is Data session The network active andthe user is termination or (MSC/BSC) may talking/non-talking.origination. or may not support the concurrent services. If the networksupports as per the IOS specification, it aims at providing concurrentservices for one voice and one 3G data session simultaneously. Withrespect to concurrent PTT service and data sessions, the DG istransparent bccause the PTT service is handled like a voice call by thenetwork/mobile.

Advanced Services

The dispatch solution architecture can be useful to build advancedservices in addition to the basic dispatch service framework. Examplesof those kinds of services are:

1. Push to Talk from IP Terminals

-   -   Push to Talk service using PTT clients on PDAs, laptops,        desktops    -   Eliminates vocoder conversion and saves RF radio channels

2. Closed Group Text Messaging

-   -   A method of using text messaging for closed user group

3. Instant Push to Talk Call Upgrade

-   -   Private Call Push to Talk call⇄Full Duplex calls on demand    -   Group Push to Talk call⇄Instant Full Duplex conferencing on        demand

4. Push to Talk message recording & playback

-   -   An efficient method of recording a copy of Push to Talk messages        for set of subscribers    -   A method of delivering and displaying the recorded Push to Talk        messages

5. Location pin point

-   -   A method to identify and distribute location of all my group        members

6. Nearest group member

-   -   A method to figure out the order list of nearest group members

7. Group /Private Voice SMS

-   -   A method of delivering and storing voice SMS applied for a        private /group basis

8. Inter Carrier Push to Talk Service

-   -   A method of allowing Push to Talk service across CDMA, GSM,        WCDMA & TDMA subscribers.    -   A method of allowing creation of dynamic group membership across        different carriers.

Call Flow for a Voice Group Call—CDMA

FIG. 7 is a diagram that illustrates the call flow for a Voice GroupCall in a CDMA network according to a preferred embodiment of thepresent invention.

-   1. The first Mobile Station (MS1) originates a group call by dialing    a Detection Point trigger code and group ID. Upon receiving the    MS1's request for an origination, the BSC formats and sends a CM    (Connection Management) Service Request message to the MSC,    prompting the MSC to begin setting up the call to the DG. The called    party IF (Information Element) contains both the Detection Point    trigger code and group ID. It is assumed that the originating DG is    also the group's Home DG.-   2. Upon receiving the CM Service Request message, the MSC analyzes    the dialed digits and determines that the trigger code in the called    party IE meets the origination trigger criteria. On satisfying the    origination trigger criteria, an ORREQ (Origination Request) message    is sent to the DG. The ORREQ contains the dialed digits.-   3. The MSC begins allocating terrestrial resources required for the    call between the BSC and the MSC, and sends CIC (Circuit Identity    Code) information in an Assignment request to the BSC.-   4. The BSC initiates the radio channel allocation procedure.-   5. Meanwhile, the DG analyzes the dialed digits and identifies the    group id. It responds to the MSC with an ORREQ message, which    contains the routing number to the DG so that the MSC can terminate    this group call to the DG.-   6. The DG gets the group id from the dialed digits received in the    ORREQ message. It obtains member information including a Mobile    Directory Number (MDN) from the group database and begins setting up    terminating legs. Based on the MDN, it sends an IAM (Initial Address    Message) message to the MSC. The terminating legs are set-up in    parallel with originating leg set-up to speed up the call set-up    time.-   7. Subsequent to the MS1 acquiring the traffic channel the BSC sends    an Assignment Complete message to the MSC.-   8. The MSC begins to route the call based on routing info (TERMLIST)    received from the DG in the ORREQ message. The MSC sends an IAM    message to the DG.-   9. The DG after receiving the LAM, immediately responds to the MSC    with an ACM (address Complete Message), and subsequently ANM (Answer    Message) with no delay between them-   10. The MSC plays an in-band ring back tone after receiving the ACM.-   11. The ANM is received by the MSC and it stops the ring back tone.-   12. Now, the DG generates an in-band chirp tone to notify the    originator to start talking. This tone is played for a specific    duration (200 msec) after which the originator starts talking.-   13. The MSC sends a paging request to the BSC in order to locate the    second Mobile Station (MS2).-   14. The BSC does the paging procedure for MS2-   15. Once a paging response is obtained from MS2, the BSC gives a    paging response to the MSC.-   16. The MSC allocates a terrestrial circuit between the MSC and BSC,    and sends the information to the BSC in an Assignment Request. The    Assignment Request message also contains the calling party number    with its group ID and signal IE for the alerting MS2.-   17. The BSC performs a traffic channel setup procedure for MS2.-   18. Subsequent to completion of the traffic channel setup, the BSC    sends an Assignment Complete message to the MSC.-   19. The BSC sends an Alert With Info message to MS2 to start    alerting. This message has the calling party number, which contains    the group ID. MS2 understands from this group ID that the call is a    PIT and ignores signal IE in this message.-   20. The MSC sends an ACM to the DG after receiving an Assignment    Complete message from the BSC, indicating that MS2 is alerting.-   21. The dispatch application at MS2 (without waiting for user    response) sends a connect message to the BSC/MSC if the dispatch    service does not require the user to press any key on the mobile to    accept the dispatch call. This provides instant connectivity between    the originating and terrmiating mobiles.-   22. The MSC sends an ANM message to the DG and the DG completes the    one-way voice path from the originating mobile to the terminating    mobile.

Call Flow for a Voice Group Call—GSM

FIG. 8 is a diagram that illustrates the call flow for a Voice GroupCall in a GSM network according to a preferred embodiment of the presentinvention.

1. MS1 requests an assignment of a dedicated signaling channel for callorigination.

2. A dedicated signaling channel is assigned and intimated to the MS1.

3. A CM Service Request is send to the MSC to initiate a call setupprocedure. Upon receiving the CM Service Request, the MSC may delay theauthentication in order to speed up the call setup.

4. The MSC sends a CM Service Accept to MS1 in order to proceed withcall setup. In this case, authentication may be initiated by the MSC ata later time.

5. MS1 sends a setup message with the dialed digits. The dialed digitscontain the access code for the group call and the group ID.

6. Because the origination trigger criteria is met as per thesubscriber's profile for PTT service, the MSC originates an Initial DP(Detection Point) Request to the DG for further service interaction.

7. After receiving the Initial DP Request from the MSC, the DG looksinto its database of group information in order to obtain directorynumbers of group members belonging to the group ID specified in themessage. For each member of the group, the DG originates an IAM andsends it to the MSC with a directory number as the called party number.The DG also sends CIC information for each terminating leg to the MSC.

8. The GSM SCF (Service Control Function) instructs the MSC to connectto the DG by specifying a redirection number.

9. The MSC triggers the assignment procedure for allocating terrestrialresources between the BSC and MSC and radio resources for MS1. MS1 isnotified about the allocated channel for this call

10. The MSC begins routing the call based on the redirection numberreceived from the GSM SCF. The MSC terminates the call to the DG bysending an IAM.

11. The DG, after receiving the IAM, immediately responds to the MSCwith an ACM, and subsequently, an ANM with no delay between them.

12. The MSC sends an Alert to MS1 to trigger alerting at MS1.

13. The DG sends an ANM to the MSC.

14. The MSC sends a connect to MS1, which stops the alerting tone atMS1.

15. Now, the DG generates an in-band chirp tone to notify the user tostart talking. This tone is played for specific duration after which theoriginator start talk.

16. The MSC send a paging request to the BSC to locate MS2.

17. The BSC performs a paging procedure to locate MS2.

18. MS2 requests a dedicated signaling channel

19. A dedicated signaling channel is assigned and intimated to MS2.

20. MS2 sends a paging response through the dedicated signaling channel.

21. When the BSC receives the paging response from MS2, it sends an MSConn Estd (Mobile Station Connection Established) message to the MSC.

22. The MSC sends a Setup message to MS2 with information such as thecalled party number and group ID.

23. MS2 responds with a Call Confirmed message to the MSC.

24. The MSC performs an assignment procedure to allocate terrestrial andradio resources.

25. After successful allocation of all resources, MS2 sends an Alertingmessage to the MSC to indicate that it is alerting.

26. The MSC sends an ACM to the DG confirming the alerting of theterminating mobile.

27. The dispatch application at MS2 (without waiting for user response)sends a Connect message to the MSC if the dispatch service does notrequire the user to press any key on the mobile to accept the dispatchcall. This provides instant connectivity between the originating andterminating mobiles.

28. The MSC sends an ANM message to the DG and the DG completes theone-way voice path from the originating mobile to terminating mobile.

Architectural Benefits

A number of benefits are derived from the architecture of the presentinvention, including, but not limited to:

1. No Change in the Network Required—The biggest advantage of thisarchitecture is that group voice services can be introduced into acarrier's existing network without requiring any changes to alreadyinstalled network equipment This just acts as an add-on facility to thecarrier. Of course, mobiles 120 require some upgrades to support thisservice.

2. Independent of Radio Access Technology—This architectural solutionsits behind the MSC 104 and interfaces with the MSC 102, through SS7 andTDM interfaces. Hence, it is independent of the radio access technologyof service provider's network. As a result, this solution can be easilyextended to GSM, CDMA, TDMA and future 3G access networks. In fact, thissolution will even work with a normal wire line interface (as itsupports TDM), thus making it capable of integrating wire line andwireless group voice services at a central node.

3. Independent of air interface—this approach does not mandatedeployment of 1×RTT, as it can work well with CDMA One. Carriers neednot accelerate capital spending on lxRIT for PIT service.

4. Superior voice quality—This architecture supports TFO so that vocoderconversion is avoided, thus increasing MOS for mobile-to-mobile calls.Also, it uses full rate EVRC.

5. Faster Call Setup—This architecture ensures faster complete callsetup time by using WIN/ANSI triggers to set up the terminating legsparallel to originating side setup. The group voice application forterminating handsets avoids unnecessary “alerting” to the user and doesnot wait for the user to “connect”. Instead, it plays a short durationtone while sending a “connect” automatically to the network. This savesusage of radio resources and makes it much mote economical than acellular call.

6. Intelligent Voice Buffering for Originating Leg—This architectureallows the PTT originating party to start talking earlier than whenactual end-to-end call setup is done. The originating party's voice isbuffered at the DG 102 until at least one of the terminating legsanswers the call This way, the originating party need not hold the PTTbutton unnecessarily until the terminating leg connects. Also, voicebuffeting starts only when a DSP (Digital Signal Processing) componentdetects voice samples on an incoming line. This reduces overall bufferspace requirements inside the DSP (since an initial silence periodbetween “listening chirp tone and start talking” is not buffered).

7. Call Support for Selective Members Within Group—This architecturesupports setting up calls for selective members within a group. The PITclient sends a list index for a group and the PHT server terminates tolisted members.

8. Mechanism of Setting Groups from Mobile Handset—This architectureallows the setting up of groups dynamically from mobiles 120. A userwith sufficient privileges can configure groups and add/delete/modifyother members. This architecture uses the SMS or IP transport toexchange messages between the PTT client and server.

9. Seamless Service Interactions: The service interaction betweencellular and dispatch is handled seamless by inherent nature of thisarchitecture.

10. Roaming across service providers: A mobile 120 can roam intodifferent service providers and still avail itself of the PIT service.The visiting MSC 104 downloads the profile from the HLR 126, when theroaming mobile 120 registers in the MSC 104. The profile contains theWIN triggers and DG 102 address for the PIT service. When the triggercriterion is met, the visiting MSC 104 contacts the DG 102 at its homenetwork. The DG 102 provides the MSC 104 with the redirection number toroute the call to the DG 102 in the home network. The DG 102 furthersets up the PIT call. This eliminates the need for the DG 102 at thevisiting network. Also, the mobile 120 can receive a group/private callwhen roaming in different networks.

11. Eliminates long distance “tromboning” effect: Tromboning refers tothe setting up of a call from the serving system of a calling party tothe home system of called party and then back to the serving system,when the called party is roaming in the serving system. If the servingsystem is capable of querying the HLR 126 for routing information of theterminating mobile, it can eliminate tromboning. The DG 102 is capableof querying the HLR 126 using IS41. When a mobile 120 roams outside hishome network (SID/NBD), the DG 102 queries the HLR 126 for its locationand sets up the call towards a DG 102 pertaining to the serving MSC 104and thus eliminates tromboning.

12. Presence Application Integration—This architecture integrates thepresence and group voice service application efficiently. Presenceinformation is useful to place call selectively to a user knowing thathe/she is available in the network

13. Wide Area Group Call Support—This architecture supports group voiceservice across regional and national boundaries. With packet networkinfrastructure at the core, long distance calls can avoid a PSIN tariff.

14. Evolution path to all IP mobile wireless communication—By alreadyimplementing IP at the core, this architecture provides an evolutionarypath for the operator to a future all-IP infrastructure. Even thoughall-IP mobile wireless is still in nascent stages for voicecommunication, this dispatch solution can be reused with minimal changesin the future for integration with a soft-switch.

15. Ubiquity of IP platforms at control and bearer plane—Since thisarchitecture uses IP based platforms for signaling and voice trafficbetween DGs 102, any IP based device with a dispatch client can utilizethe dispatch services and reach the wireless group users and vice versa.This provides a true convergence of instant messaging services betweenwire-line and wireless users. Also, IP based dispatch platforms can beintegrated easily with already existing instant messaging and presenceservers within the Internet

16. PTT support for landline—Since the DG 102 is connected to thePSTN/106 network, it can very easily support landline subscribers aspart of a dispatch group. The landline users can originate and terminatea PIT call.

17. Usage of multicasting reduces number of voice packets in thenetwork—By using dynamic multicasting for a group call, the number of(bearer) packets flowing in the backbone intranet can be reducedsignificantly for inter-DG dispatch calls. This architecture proposes amulticast based approach for the members who are in within the subnet(but across the DG 102). In this way, the number of packets flowing onthe bearer plane in the IP network 124 can be drastically reduced withinthe subnet However, for a member of a group call outside the subnet, itis intended to use unicast, since router updates may take a significantamount of signaling time for setting up a dynamic group call.

Conclusion

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not with this detailed description, but rather bythe claims appended hereto.

1. A dispatch service apparatus for providing group voice services in awireless network, comprising: a wireless network for making callsbetween mobiles, wherein the calls are initiated by call setup andin-band signaling within the wireless network and voice frames for thecalls are switched between the mobiles across bearer paths in thewireless network; and a dispatch gateway that interfaces to the wirelessnetwork to provide group voice services therein, wherein both thedispatch gateway and the mobiles that use the group voice servicescommunicate with each other using the call setup and in-band signalingwithin the wireless network, and the dispatch gateway switches the voiceframes for the group voice services from an originating mobile to allterminating mobiles across the bearer paths in the wireless network. 2.The dispatch service apparatus of claim 1, wherein the dispatch gatewayprovides instant two-way half-duplex voice messaging within a group ofusers of the wireless network.
 3. The dispatch service apparatus ofclaim 1, wherein the group voice services comprises a Push To Talk (PTT)service.
 4. The dispatch service apparatus of claim 1, wherein thedispatch gateway interfaces with a group and subscriber database forretrieving group and subscriber related information, and for validatingmembers' authenticity.
 5. The dispatch service apparatus of claim 4,wherein the group related information is stored in the group databasekeyed against a unique group id.
 6. The dispatch service apparatus ofclaim 4, wherein the group related information comprises a set ofsubscribed members and their privileges.
 7. The dispatch serviceapparatus of claim 4, wherein subscriber related information is storedin the subscriber database keyed against a mobile identifier or memberid.
 8. The dispatch service apparatus of claim 4, wherein the group andsubscriber database is distributed across multiple dispatch gateways tosupport nationwide group voice services.
 9. The dispatch serviceapparatus of claim 1, wherein the dispatch gateway handles registrationrequests and updates group members with presence information for fellowgroup members.
 10. The dispatch service apparatus of claim 1, wherein aregistration and presence application enables group members to track apresence of fellow members in the wireless network.
 11. The dispatchservice apparatus of claim 1, wherein the wireless network sets up acall between a mobile and the dispatch gateway, and the dispatch gatewayinteracts with the mobile across the network through DTMF signaling onthe call.
 12. The dispatch service apparatus of claim 1, wherein thedispatch gateway performs call setup for selected members within agroup.
 13. The dispatch service apparatus of claim 1, wherein thedispatch gateway performs call setup on terminating legs in parallelwith a call setup for an originating leg.
 14. The dispatch serviceapparatus of claim 1, wherein the dispatch gateway performs intelligentvoice buffering for an originating leg of a group call.
 15. The dispatchservice apparatus of claim 1, wherein the dispatch gateway exchanges aset of defined in-band DTMF tones with a mobile within the wirelessnetwork as call control events to regulate a group call.
 16. Thedispatch service apparatus of claim 1, wherein the dispatch gatewaycontrols a floor of a group call by allowing only one member to speak atany time during a group call.
 17. The dispatch service apparatus ofclaim 1, wherein the dispatch gateway provides voice frame duplicationfor a group call.
 18. The dispatch service apparatus of claim 1, whereinthe dispatch gateway performs dynamic multicasting of voice frames for agroup call involving multiple dispatch gateways.
 19. The dispatchservice apparatus of claim 1, wherein the dispatch gateway performsvocoder conversion on one or more legs of a group call.
 20. The dispatchservice apparatus of claim 1, wherein the dispatch gateway isindependent of the wireless network's radio access technology.
 21. Thedispatch service apparatus of claim 1, wherein the dispatch gatewaycommunicates with other dispatch gateways.
 22. The dispatch serviceapparatus of claim 21, wherein the dispatch gateways support group voiceservices across network, regional and national boundaries.
 23. Thedispatch service apparatus of claim 1, wherein the mobile includes adispatch application.
 24. The dispatch service apparatus of claim 1,wherein the mobile can administer dispatch services provided by thedispatch gateway.
 25. The dispatch service apparatus of claim 1, whereinthe mobile can roam across a plurality of wireless networks and stillparticipate in the group voice services.
 26. The dispatch serviceapparatus of claim 1, wherein the dispatch gateway performs optimalrouting to terminate group voice calls for subscribers roaming outsideof their home networks.